The traditional floor finishing process for providing a smooth dense floor typically associated with interior cast-in-place concrete, terrazzo, epoxy or co-polymer flooring involves using hand or mechanical power troweling. Power troweling machines are available in two basic styles: walk-behind and ride-on. These machines have, historically, been fitted with various types of steel blades or, more recently, plastic blades, for different aspects of the finishing process.
Most walk-behind power trowels include a single set of horizontal rotating blades encircled by a guard ring cage, a gas or electric engine and a handle for machine control and steering. The blades are attached to radially extending, spaced apart arms of a spider assembly or rotor, which is caused to rotate by a shaft driven by the engine. Each rotor typically mounts three- or four-blades and has a diameter ranging from 2 to 5 feet, giving a finished area per revolution of slightly more than 3 to almost 20 square feet. A typical 36-inch diameter walk-behind power trowel can finish 7000 to 15,000 square feet of concrete per day. Since walk-behind power trowels weigh less than ride-on trowels, they can be put on slabs sooner than their heavier counterparts. Even so, concrete needs to be a bit harder before power troweling than hand troweling.
Configured with either two or three sets of rotating blades, typical ride-on power trowels range in size from approximately 6 feet to slightly more than 10 feet in path width, to produce a troweled area of about 17 to 40 square feet, respectively. The largest units weigh more than a ton and can finish about 30,000 square feet per day. Ride-on trowels can be configured with two or more rotors, each having a plurality of radially oriented, spaced-apart blades. The blades on adjacent rotors may be overlapping or non-overlapping. Overlapping blades are spaced so that each set of blades overlaps slightly with the other set as the blades rotate. Because the two sets overlap, no unfinished concrete is left between them, as is the case with a non-overlapping configuration.
There are three basic types of blades for both walk-behind and ride-on trowels: float, finish and combination. Float blades are normally about ten inches wide and are intended to run flat on the concrete shortly after the concrete has been poured and screeded. The blades, which have their leading edges turned up slightly so that fresh concrete won't be damaged, push aggregate down into the concrete and bring water to the surface. Finishing blades are used after floating is completed. They, typically, are rectangular in shape with the opposite long sides serving as the finishing edges. About six inches wide, they are pitched during use to apply more pressure to the concrete than with float blades, so that the surface can be compacted. The pitch angles for finishing blades are increased slightly on each successive pass to put increasingly greater pressure on the concrete surface. If the blades are pitched too much, a washboard effect may result, necessitating reducing the blades' pitch and refinishing the surface. Combination blades can both float and finish. They are, typically, about 8 inches wide, and are a combination of floating and finishing blades. They have a finishing edge and a float edge, are normally wider than finishing blades but narrower than float blades, and are more expensive than either finishing or floating blades. Combination blades are popular because operators don't have to stop and change the blades on each rotor for each operation. Their disadvantage is that they are not as efficient at either floating or finishing as the blades designed specifically for these jobs. One edge of the combination blade is pitched upwardly for floating, the pitched edge allowing fresh concrete to flow under the blade during floating, and the opposite edge is flat for finishing.
Mounting systems for mounting the blades, whether float, finish or combination, to the trowel arms on the rotors vary. In many systems, blades are bolted directly to the trowel arm. In other systems, the blades are connected to a mounting bar and the bar is bolted to the trowel arm.
During the final stage of finishing, a finish or combination blade is used to provide a smooth, dense finish. During this stage, burnish marks can occur on the finish, which are generally caused by the steel from which these blades have historically been made. In the past, to avoid these burnish marks, power troweling would have to stop and hand finishing would have to be used to complete the finishing process, which is both time and labor intensive. One relatively recent solution to the burnishing problem has been substituting plastic for steel as the material for the finishing blades. However, in most instances, the plastic blades are not strong or rigid enough to finish the concrete floor to an optimum level. Moreover, plastic blades can only be used on walk-behind trowels, as the ride-on trowels are much too heavy for the plastic blades.
Accordingly, there still exists a need for a stronger, more rigid blade that can be used on both styles of power trowels while also providing a burnish-free finish for many different types of floor systems.